The present invention relates to an ultrasonic equipment, and more particularly to a phasing circuit for signals derived from a received ultrasonic wave used in a scanning type ultrasonic equipment provided with a probe including a plurality of transducer elements and with a phasing circuit for signals caused by a received ultrasonic wave, such as an ultrasonic diagnostic equipment of electric sector scanning type.
The ultrasonic diagnostic equipment of electronic sector scanning type uses a probe such as shown in FIG. 1. That is, a probe P includes a plurality of transducer elements B juxtaposed on a sound absorbing material A, and the number of juxtaposed transducer elements per unit length is made as large as possible, to generate an ultrasonic beam having good directional characteristics.
Further, in order to emit an ultrasonic beam in a desired direction, pulse generators connected to the probe P are constructed such that they are connected to counters, the number of which is equal to the number of transducer elements, and that the timing of driving each transducer element is controlled by a train of pulses generated by a corresponding one of the counters. When formed of an integrated circuit, such a pulse generator can be made small in size and low in cost. (Reference may be made to a Japanese Patent Application Specification Publication No. 42293/81).
Recently, in order to make the above pulse generator more small-sized and inexpensive, a custom gate array LSI is used for forming the pulse generator, in place of a general-purpose integrated circuit.
Now, turning to the ultrasonic wave receiving section, analog signals are delivered from the transducer elements on the basis of a received ultrasonic wave, and a variable delay circuit which is complicated, large-sized and expensive, is required to delay the received signals from each transducer element in accordance with desired directional characteristics of the probe in a received ultrasonic wave.
In order to delay the signals from the transducer elements in accordance with the direction of the directional characteristic of the probe in the received ultrasonic wave, and to make small the number of parts included in the delay circuit, it has been proposed to use a phasing circuit such as shown in FIG. 2. In this phasing circuit, as shown in FIG. 2, input terminals .circle.1 , .circle.2 , . . . and .circle.n of delay circuits 1, each of which is formed of a lumped constant type LC delay line having taps, are applied with voltage signals from transducer elements B.sub.1, B.sub.2, . . . and B.sub.n (not shown), respectively. Each delay circuit 1 has a structure shown in FIG. 3. That is, a delay line is made up of a number of inductors L and capacitors C, and taps T.sub.1, T.sub.2, . . . and T.sub.n of the delay line are connected to electronic switches S.sub.1, S.sub.2, . . . and S.sub.n, respectively. Thus, the delay time of the delay line can be controlled in such a manner that one of the taps is selected by turning on a corresponding one of the electronic switches. Each delay circuit 1 is used to obtain a relatively short delay time. Incidentally, in FIG. 3, reference character R designates resistors, and reference numeral 5 an amplifier.
Referring back to FIG. 2, the output voltages of one set of three delay circuits 1 are applied to one of adders 2, to be added to each other. The output voltage of each adder 2 is applied to one of delay circuits 3 each having a long delay time, to be delayed by a predetermined time. The output voltages of the delay circuits 3 are applied to an adder 4, to be added to each other. A maximum delay time obtained by the delay circuit 1 is dependent upon a delay time between adjacent ones of the taps T.sub.1, T.sub.2, . . . and T.sub.n of the delay line, and the delay time between adjacent taps is the resolution of the delay circuit 3. In other words, the delay time resolution of the variable delay circuit shown in FIG. 2 is given by the delay time resolution of the delay circuit 1, that is, the delay time between adjacent taps of the delay line shown in FIG. 3.
FIG. 4 shows a delay time which is given to each of the signals from the transducer elements B.sub.1 through B.sub.n when an ultrasonic beam has been deflected by an angle of .theta., and shows how the delay time is allotted to the delay circuits 1 and 3. Referring to FIG. 4, periods t.sub.12, t.sub.13 ... and t.sub.19 are given by the delay circuits 1, and periods t.sub.32 and t.sub.33 are given by the delay circuits 3. For instance, the signal voltages from the transducer elements B.sub.4, B.sub.5 and B.sub.6 are applied to the delay circuits 1, to be delayed by the periods t.sub.14, t.sub.15 and t.sub.16, respectively. The signal voltages thus delayed are added to each other, and the resultant signal thus obtained is applied to the delay circuit 3, to be delayed by the period t.sub.32.
According to the above system, the number of delay circuits which are required for giving long delay periods to the signal voltages, is equal to one-third the number of delay circuits required in the case where the signal voltages from the transducer elements B.sub.1 through B.sub.n are individually given long delay periods. That is, the above system can make the phasing circuit small in size and low in cost.
Further, the number of delay circuits 3 can be reduced by increasing the number of delay circuits 1 connected to one adder 2. In this case, however, the delay time of the delay circuit 1 becomes long, and it is required to increase the taps of the delay line shown in FIG. 3, in order not to reduce the delay time resolution. Accordingly, the number of delay circuits 3 is determined on the basis of a desired delay time resolution and a required limit of cost.
In addition to the phasing circuit shown in FIGS. 2 to 4 for delayinq signal voltages which result from a received ultrasonic wave, such a circuit as shown in FIG. 5 has been proposed. (Refer to the "Proceedings of the Japan Society of Ultrasonics in Medicine", May, 1976, page 111, and a Japanese Patent application Laid-open No. 102621/77.)
In FIG. 5, reference character 5' designates amplifiers for amplifying signals from transducer elements B.sub.l through B.sub.n of a probe, and S a switching circuit for selecting one of two connection modes; in one connection mode, the signals from terminals .circle.1 , .circle.2 , . . . and .circle.n are sequentially supplied to output terminals O.sub.1, O.sub.2, . . . O.sub.n, respectively, in that order, and in another connection mode, the signals from the terminals .circle.1 , .circle.2 , . . . and .circle.n are sequentially supplied to the output terminals O.sub.n, O.sub.n-1, . . . and O.sub.1, respectively, in that order. Output signals from the output terminals are applied to a circuit made up of delay lines 1' and adders 2'. Thus, the signals from the terminals .circle.1 through .circle.n are successively added to each other, after each of these signals having been delayed by a predetermined time. The delay time giving each of the signals at each delay line 1' can be varied in such a manner that one of taps included in the delay line is selected by a control signal CS.
Further, a phasing circuit which is somewhat different in technical thought from but similar in circuit construction to the circuit of FIG. 5, has been proposed. This phasing circuit also uses an LC delay line with taps. (Refer to IEEE, Ultrasonic Symposium, 1980, page 757.)
In the case where a probe having a diameter of about 16 mm includes 48 or 64 transducer elements, the delay system shown in FIG. 2 usually includes 12 or 20 delay lines each having a delay time of 4 to 5 nsec. When an ultrasonic wave having a frequency of 2 to 3.5 MHz is generated and utilized, a ratio of the size of the delay lines to that of the ultrasonic equipment and a ratio of the cost of the delay lines to that of the ultrasonic equipment become large. Accordingly, it is difficult to make the ultrasonic equipment small in size and low in cost.